This disclosure is directed to flame retardant thermoplastic compositions comprising polycarbonate, their method of manufacture, and methods of use thereof and in particular to thermoplastic polycarbonate copolymer compositions having low smoke density and low heat release.
Polycarbonates are useful in a wide variety of applications at least in part because of their good balance of properties, such as moldability, heat resistance and impact properties among others. However, standards for flame retardancy properties such as flame spread, heat release, and smoke generation upon burning have become increasingly stringent, particularly in applications used in mass transportation (aircraft, trains, and ships), as well as building and construction. For example, the European Union has approved the introduction of a new harmonized fire standard for rail applications, namely EN-45545, to replace all currently active different standards in each member state. This standard will impose stringent requirements on heat release and smoke density properties allowed for materials used in these applications. Smoke density (Ds-4) in EN-45545 is the smoke density after four minutes determined in accordance with ISO 5659-2, and heat release in EN-45545 is the maximum average rate of heat emission (MAHRE) determined in accordance with ISO 5660-1.
It is exceptionally challenging to develop materials that meet stringent smoke density standards and heat release standards in addition to other material requirements. It is particularly challenging to develop materials that meet these standards and that have good mechanical properties (especially impact/scratch resistance) and processability. Accordingly there remains a need for thermoplastic compositions that have a combination of low smoke and low heat release properties. It would be a further advantage the compositions could be rendered low smoke and low heat release without a significant detrimental effect on one or more of material cost, processability, and mechanical properties. It would be a still further advantage if the materials could be readily thermoformed or injection molded. It would be a still further advantage if such materials were in compliance with European Railway standard EN-45545, for example, without having a detrimental effect on material cost, processability, and mechanical properties.